It has been known to set up parameters for recording speed by linear functions (see Patent Literatures 1 to 3). Particularly, a technique of changing parameters stepwise has been disclosed in the Patent Literatures 2 and 3.
However, it has not been mentioned that the length of at least either of final heating pulses and final cooling pulses (irradiation time) is discontinuously changed.
Rewritable optical disks applied with a phase-changing technique, which are represented by CD-RW, DVD-RW, DVD+RW, etc., have been widely popularized for audio/visual purposes and the information recording purpose of computers. Moreover, improvement of the recording speed onto these optical disks has been anticipated with an increasing capacity of digital information in recent years. Both rewriting performance at a higher scanning speed and rewriting performance in a broader scanning speed range are required for high-speed recording onto optical disks using such a phase-changing technique. The former is the highest recording speed and the latter is equivalent to a recordable speed range. Particularly, the latter corresponds to a CAV (Constant Angular Velocity) recording which is a technique necessary for accelerating random access recording; hence a scale of speed (highest speed/lowest speed) of about 2.4 folds is necessary. Moreover, in the CAV recording, the recording scanning speed v changes corresponding to the recording radius position r, namely, v/r=constant, therefore it must be recordable at any recording speed below the highest recording speed. Furthermore, if the highest speed increases, the scanning speed range also inevitably broadens. For example, in a 4× speed disk of DVD+RW, the scanning speed range of 5.8 to 14.0 m/s is required for the CAV, but in a 8× speed disk, the scanning speed range of 11.6 to 27.9 m/s is required, therefore, the development of such an optical recording medium capable of recording in a very wide range, which can correspond to the 8-hold speed disk, and a recording method of the optical recording medium have been desired.
On the other hand, recording layer material must be changed to material suitable for even higher speed recordings in order to increase the highest recording speed. Usually, a phase-change material is used for the recording layer material of optical disks represented by DVD+RW. For example, in general, the phase change material is made of alloys capable of reversibly changing the phase between an amorphous phase and a crystalline phase. In increasing the recording speed, a phase-change material having a high crystallization rate must be used to accelerate the phase change between the amorphous phase and the crystalline phase.
However, to increase the crystallization rate results in the great difficulty in controlling the crystalline phase at the time of low-speed recording. Therefore, recording methods (strategies) in a speed region close to the highest recording speed and a speed region close to the lowest recording speed must be greatly changed. Hence, there is the problem that it becomes very difficult to record at any recording speed below the highest recording speed if using a recording layer material able to correspond to the high-speed recording.
Patent Literature 1 Japanese Patent Application Laid-Open No. 2000-322740
Patent Literature 2 Japanese Patent Application Laid-Open No. 2001-118245
Patent Literature 3 Japanese Patent Application Laid-Open No. 2001-243626